1911 Encyclopædia Britannica/Rheticus
RHETICUS, or Rhaeticus (1514–1576), a surname given to George Joachim, German astronomer and mathematician, from his birth at Feldkirch in that part of Tirol which was anciently the territory of the Rhaeti. Born on the 15th of February 1514, he studied at Tiguri with Oswald Mycone, and afterwards went to Wittenberg where he was appointed professor of mathematics in 1537. Being greatly attracted by the new Copernican theory, he resigned the professorship in 1539, and went to Frauenberg to associate himself with Copernicus, Nicolaus (q.v.), and superintended the printing of the De Orbium Revolutione which he had persuaded Copernicus to complete. Rheticus now began his great treatise, Opus Palatinum de Triangulis, and continued to work at it while he occupied his old chair at Wittenberg, and indeed up to his death at Cassovia in Hungary, on the 4th of December 1576. The Opus Palatinum of Rheticus was published by Valentine Otho, mathematician to the electoral prince palatine, in 1596. It gives tables of sines and cosines, tangents, &c., for every 10 seconds, calculated to ten places. He had projected a table of the same kind to fifteen places, but did not live to complete it. The sine table, however, was afterwards published on this scale under the name of Thesaurus Mathematicus (Frankfort, 1613) by B. Pitiscus (1561–1613), who himself carried the calculation of a few of the earlier sines to twenty-two places. He also published Narratio de Libris Revolutionum Copernici (Gedenum, 1540), which was subsequently added to editions of Copernicus's works; and Ephemerides until 1551, which were founded on the Copernican doctrines. He projected numerous other Works, as is shown by a letter to Peter Ramus in 1568, which Adrian Romanus inserted in the preface to his Idea of Mathematics.